Selection Logic

Neutron Spectrum

Coolant

Fuel PinGeometry Loop

Configuration

Accident Response

Energy Conversion

Specific Mass Specific

Area

Safety

Nuclear Core Issues

Reactor Type Mean Neutron Energy ExamplesFast 0.30 MeV SP-100, Cosmos-1900

Epithermal 1-10 eV Rover (NERVA)Thermal 0.05-0.1 eV SNAP-10A, TOPAZ

Key Differences-Thermal vs Fast Reactors

• Low 235U Critical Mass for Thermal Reactor

- Advantage where unit cost is paramount or many units are required

- Unsuitable for long life time, very high power reactorsOverly large burn-up fractionLoss of control capabilityFuel degradation

• Hydrogen Moderated Reactors Temperature Limited(900 to 950 °K unless moderator is separately cooled)

• Beryllium Moderated reactors Similarly Limited in Temperature(Helium Formation)

• Graphite (Carbon) Moderated Reactors large and Relatively Heavy

• Fast Reactor Restart Not Limited by Fission Product Poisoning

• Compactness Favors High Fuel Density Fast Reactor Designs------------------------------------------------------------------------------------------

Fissile Fuel Depletion

• 1 MWd (thermal) ≈ 1 g 235U burned

• 7 years at 2.0 MWt ≈ 5 kg 235U burned

This is:

50% of 235U loading of 2.0 MWt Thermal Reactor

3% of 235U loading of 2.0 MWt Fast Reactor

300025002000150010005000

Thermoelectric

Rankine-Organic

Rankine-Hg

Rankine-K

Brayton

Stirling

Thermionics -in core

Thermionic-out of core

Amtec

Operating Temperature Range for SP-100 Power Conversion Schemes

Temperature ° K

35302520151050

Thermionic-out of core

Thermoelectric

Rankine-Hg

Thermionics -in core

Brayton

Rankine-Organic

Rankine-K

Stirling

Amtec

5

5.4

7

10

18.6

20

20

25.4

28.5

Conversion Efficiencies for SP-100 Systems

Efficiency-%

Mass Distribution of SP-100 Power Source (1988)

Shield

Heat Rejection

Reactor

Primary Ht.Transport

Structural

Power Conv.

Power Conditioning

I & C

23 %

19 %

15 %

12 %

10 %

8%

7%

7 %

Total Mass = 5422 kg